JPH04202070A - Siliceous porous body and its production - Google Patents

Abstract

PURPOSE:To enhance strength by mixing crystalline SiO2 powder with a prescribed amt. of amorphous SiO2 powder of a specified average particle diameter, molding and firing the mixture. CONSTITUTION:The particle diameter of silica powder made of high purity crystalline SiO2 is regulated to 20-30mum. Amorphous SiO2 powder whose particle diameter is <=1/2 of that of the silica powder is produced by hydrolyzing starting material such as ethyl silicate and firing the resulting precipitate. The silica powder is mixed with 5-50wt.% of the amorphous SiO2 powder and this mixture is press-molded into a prescribed shape and fired at 1,300-1,500 deg.C. The crystalline SiO2 particles are densely bonded with the amorphous SiO2 powder while leaving many open pores among the crystalline SiO2 particles and a porous SiO2 body having high strength is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a siliceous porous material used for filtration of liquids and gases, and a method for producing the same.

[Prior art] Siliceous porous materials have excellent chemical resistance and do not contain harmful elements that affect the characteristics of semiconductor devices, so they can be used as filters for various liquids and gases necessary for semiconductor device manufacturing. Attention has been paid.

For this purpose, (1) high purity, (2) high porosity and excellent fluid permeability, (3) uniform bore diameter, ( 4) It is necessary that the porous body has high mechanical strength.

Conventionally, this type of siliceous porous material includes sintered glass manufactured by sintering siliceous powder whose particle size is adjusted as necessary, such as quartz glass powder, under conditions where pores remain.
Alternatively, a so-called Vycor glass porous material is known in which porous silica is obtained by dissolving soluble components of phase-separated glass.

[Problems to be Solved by the Invention] However, it is difficult to obtain a strong sintered body of sintered glass unless the temperature is raised to a point where the quartz glass powder particles themselves that form the skeleton soften and flow. . As a result, the pore diameters become uneven and the porosity becomes small, making it impossible to reduce the fluid permeation resistance.

Therefore, it is known that particles are sintered while retaining the entire skeleton by adding a sintering aid such as boron oxide to increase the fluidity of the particle surface. This may contaminate the filtration fluid, which is not preferable for use in semiconductor manufacturing processes, etc.

In addition, the Vycor porous material has residual impurities such as alkali and boron, and its permeability and mechanical strength are not fully satisfactory.

Therefore, an object of the present invention is to provide a porous siliceous material having high purity, high porosity, excellent fluid permeability, uniform pore diameter, and high mechanical strength, and a method for producing the same.

[Means for Solving the Problems] In order to solve the above problems, the siliceous porous body of the first invention has crystalline silica powder particles tightly bonded by an amorphous silica layer covering the surface thereof, and It is constructed by forming a large number of open pores between crystalline silica powder particles.

A second invention is the method for producing a siliceous porous material according to the first invention, wherein the crystalline silica powder includes amorphous silica powder having an average particle size of 1/2 or less of the crystalline silica powder particles. This is a method in which 5 to 50% by weight of is added, mixed, molded, and then fired at a temperature of 1300 to 1500°C.

[Operation] In the above means, the crystalline silica powder particles are bonded together by the amorphous silica layer (silica glass layer) covering the surface thereof to form the skeleton of the porous substrate.

As the crystalline silica powder, crushed silica stone or crystal is used, and as the amorphous silica powder, quartz glass powder,
Synthetic silica powder or the like is used.

When the average particle size of the amorphous silica powder exceeds 1/2 of the crystalline silica powder particles, the amorphous silica powder softens and the flow rate is not large, so the amorphous silica becomes crystalline silica powder. It does not spread over the entire surface of the body particles and remains in lumps, causing clogging.

Furthermore, if the amount of amorphous silica powder added exceeds 50% by weight, a structure will appear in which crystalline silica is embedded, and the crystalline silica powder particles will not form the framework of the porous substrate, If it is less than %, an amorphous silica layer will not be formed on the entire particle surface of the crystalline silica powder, and sufficient mechanical strength will not be obtained.

If the firing temperature is less than 1,300°C, the amorphous silica powder will soften and become difficult to flow, and if it exceeds 1,500°C, the crystalline silica powder will also be softened and deformed, impairing the formation of the skeleton of the porous substrate.

[Example] Examples of the present invention will be described in detail below.

Example 1 The particle size of silica powder made of silica (Sio2) with a purity of 99% or more was adjusted by water testing to have a particle size of 20 to 30 μm. According to X-ray diffraction, this silica powder was composed of α-quartz crystals.

On the other hand, ethyl silicate was hydrolyzed in the presence of ammonia, and the resulting precipitate was calcined at a temperature of 450°C to obtain amorphous silica powder. This powder consisted of particles of approximately 0.1 μm.

Next, 20 parts by weight of amorphous silica powder was mixed with 100 parts by weight of the silica powder, and the mixture was press-molded into a disk shape with a diameter of 30 mm and a thickness of 5 mm, and a length of 5 mm and a width of 5 mm.
, molded into a rod shape with a length of 60 mm, and heated at a temperature of 1400°C for 2 hours.
A disk-shaped sample and a rod-shaped sample were obtained by firing for a time.

When examining the air permeability of the disc-shaped sample, we found that
The differential pressure is 100 at an air flow rate of 10 mu/min, am2.
It showed a good value of mmTorr.

The pore distribution was examined by mercury porosimetry, and the average diameter was 3 μm, within a range of ±10%.

On the other hand, when we measured the bending strength of the rod-shaped sample, we found that 3
The pressure was 0 to 50 MPa, which is a very large value for a porous material. Then, the fracture surface was examined using an SEM (scanning electron microscope).
When observed, the amorphous silica powder softens, and a fluidized amorphous silica layer is formed on the surface of the silica powder particles, and the amorphous silica gathers at the contact area between the silica powder particles, forming a neck. I found out that I was gaining weight in my midsection.

Example 2 Crystalline and amorphous silica raw materials were prepared in the same manner as in Example 1, mixed in various proportions as shown in Table 1, and fired under various temperature conditions. Table 1 shows the air permeability and strength of each sample obtained in comparison with that of Example 1. If both air permeability and strength were 0.1 or less, the objectives could not be achieved.

Table 1 Therefore, the amount of amorphous silica powder added to the crystalline silica powder was set at 5 to 50% by weight, and the firing temperature was set at 1300 to 1.
It can be seen that the temperature should be 500°C.

Example 3 Quartz crystal powder with a purity of 99% or higher was adjusted to a particle size of 100 μm±10%, while quartz glass was ground and adjusted to various particle sizes as shown in Table 2.

Quartz glass powder of various particle sizes was added to the above crystal powder in the proportions shown in Table 2, and the mixture was press-molded into the same shape as in Example 1, and then fired at a temperature of 15,000°C for 3 hours to obtain various disc-shaped and rod-shaped samples. A sample was obtained.

The air permeability and strength of each sample obtained are shown in Table 2 in comparison with those of Example 1.

In this example, since the particle size of the crystal powder was large, the purpose could not be achieved if the air permeability was less than 1.

Table 2 Therefore, it can be seen that the particle size of the amorphous silica powder particles should be set to 1/2 or less of that of the crystalline silica powder.

[Effects of the Invention] As described above, according to the present invention, the crystalline silica powder particles are bonded by the amorphous silica layer covering the surface to form the skeleton of the porous substrate, so that the porosity and pore diameter are can be controlled with good reproducibility, mechanical strength can be increased, and unlike conventional methods, components other than silica are not included, making it possible to obtain a porous body of extremely high purity.

Applicant: Toshiba Ceramics Corporation

Claims (2)

[Claims] (1) A silica characterized in that crystalline silica powder particles are tightly bonded by an amorphous silica layer covering the surface thereof, and a large number of open pores are formed between the crystalline silica powder particles. porous material. (2) 5 to 50% by weight of amorphous silica powder with an average particle size of 1/2 or less of the crystalline silica powder particles is added to the crystalline silica powder.
A method for producing a porous siliceous material, which comprises adding, mixing, shaping, and then firing at a temperature of 1,300 to 1,500°C.